The depression worksheets calculation method only results in the entered annual depreciation when the worksheet is used to calculate exactly one year at a time.
At the beginning and end of an assets life one calculation can be done to estimate the full part year depreciation, To do this Managers worksheet uses a linear approximation (of the underlying multi year exponential decrease in asset value).
For all other time periods external manual calculation of depreciation is required.
For more extensive discussion see Depreciation calculation is not correct - #17 by Patch